A $U$-Spin Anomaly in Charm CP Violation

Abstract

Recent LHCb data shows that the direct CP asymmetries of the decay modes $D^0\to {\pi }^{+}{\pi }^{-}$ and $D^0\to K^{+}{K}^{-}$ have the same sign, violating an improved $U$-spin limit sum rule in an unexpected way at $2.1\sigma$. From the new data, we determine for the first time the imaginary part of the CKM-subleading, $U$-spin breaking $\Delta U=1$ correction to the $U$-spin limit $\Delta U=0$ amplitude. The imaginary part of the $\Delta U=0$ amplitude is determined by $\Delta a_{CP}^{\mathrm{dir}}$. The corresponding strong phases are yet unknown and could be extracted in the future from time-dependent measurements. Assuming $\mathcal{O}(1)$ strong phases due to non-perturbative rescattering, we find the ratio of $U$-spin breaking to $U$-spin limit contributions to the CKM-subleading amplitudes to be $(173_{-74}^{+85})\%$. This highly exceeds the Standard Model (SM) expectation of $\sim 30\%$ $U$-spin breaking, with a significance of $1.95\sigma$. If this puzzle is confirmed with more data in the future, in the SM it would imply the breakdown of the $U$-spin expansion in CKM-subleading amplitudes of charm decays. The other solution are new physics models that generate an additional $\Delta U=1$ operator, leaving the $U$-spin power expansion intact. Examples for the latter option are an extended scalar sector or flavorful $Z^{\prime }$ models.

20 pages. Matches published version

References in corpus (13)

• FLAG Review 2021
• New Physics and CP Violation in Singly Cabibbo Suppressed D Decays
• Branching ratios and direct CP asymmetries in $D\to PP$ decays
• Charm Meson Decays
• Revisiting CP violation in $D\to PP$ and $VP$ decays
• Testing New Indirect CP Violation
• Topological amplitudes in $D$ decays to two pseudoscalars: a global analysis with linear $SU(3{)}_F$ breaking
• Direct CP asymmetry in $D\to {\pi }^{-}{\pi }^{+}$ and $D\to K^{-}{K}^{+}$ in QCD-based approach
• On $SU(3{)}_F$ Breaking through Final State Interactions and CP Asymmetries in $D\to PP$ Decays
• Enhancement of charm CP violation due to nearby resonances
• $CP$ asymmetries in charm decays into neutral kaons
• Neutral $D\to K{K}^{\ast }$ decays as discovery channels for charm CP violation
• The Mathematical Structure of $U$-Spin Amplitude Sum Rules

Cited by in corpus (13)

• Final-state interactions in the CP asymmetries of charm-meson two-body decays
• Two is better than one: The U-spin-CP anomaly in charm
• Large CP violation in charmed baryon decays
• Implications of recent LHCb data on CPV in b-baryon four body decays
• Measurement of the time-integrated CP asymmetry in $D^0\to K_S^0{K}_S^0$ decays using Belle and Belle II data
• Implications of the evidence for direct $\mathbf{CP}$ violation in $D\to {\pi }^{+}{\pi }^{-}$ decays
• Measurement of the CP asymmetry in $D^{+}\to {\pi }^{+}{\pi }^0$ decays at Belle II
• Measurement of the time-integrated $CP$ asymmetry in $D^0\to K_{\mathrm{S}}^0{K}_{\mathrm{S}}^0$ decays using opposite-side flavor tagging at Belle and Belle II
• Measurement of $CP$ asymmetry in $D^0\to K_{\mathrm{S}}^0{K}_{\mathrm{S}}^0$ decays with Run 3 data
• Search for $CP$ violation in ${\Xi }_c^{+}\to {\Sigma }^{+}{h}^{+}{h}^{-}$ and ${\Lambda }_c^{+}\to p{h}^{+}{h}^{-}$ at Belle II
• Measurement of the time-integrated $CP$ asymmetry in $D^0\to {\pi }^0{\pi }^0$ decays at Belle II
• Search for $CP$ violation in $D_{(s)}^{+}\to K_S^0{K}^{-}{\pi }^{+}{\pi }^{+}$ decays using triple and quadruple products
• Polarisation fractions in $B\to V_1{V}_2$: U-Spin constraints and new physics signatures